中文摘要：

【目的】断奶前后犊牛胃肠发育及其吸收与代谢功能会发生明显改变,尤其是断奶前的饲养管理显著影响犊牛胃肠的发育乃至以后的生产性能。2-甲基丁酸是一种短链支链挥发性脂肪酸,在瘤胃内主要来自于支链氨基酸的降解,可以作为反刍动物胃肠发育的调控剂。因此,通过研究2-甲基丁酸对断奶前后犊牛小肠消化酶活性、小肠黏膜生长激素受体和钠-葡萄糖共转运载体m RNA表达的影响,揭示2-甲基丁酸对犊牛小肠发育的作用机理。【方法】试验选用32头体重（44.7±0.3）kg、发育正常的15日龄哺乳荷斯坦公犊,随机分为4组,每组8头,对照组饲喂基础日粮,试验组分别在基础日粮基础上添加2-甲基丁酸3、6和9 g·d^-1。所有犊牛在45日龄断奶,分别于断奶前（30日龄）和断奶后（90日龄）从各组抽取4头,晨饲前称重后进行屠宰,采集十二指肠、空肠近端1/4处、空肠远端1/4处和回肠末端的内容物,采用比色法测定乳糖酶、淀粉酶、脂肪酶和胰蛋白酶的活性,采集十二指肠、空肠近端1/4处、空肠远端1/4处和回肠末端黏膜组织,采用实时荧光定量PCR技术检测小肠黏膜组织生长激素受体（GHR）和钠-葡萄糖共转运载体（SGLT^-1）m RNA的表达。【结果】断奶后犊牛小肠各段乳糖酶活性显著低于断奶前,而断奶后犊牛小肠各段淀粉酶、脂肪酶和胰蛋白酶活性却显著高于断奶前。日粮添加2-甲基丁酸6和9 g·d^-1后,较3 g·d^-1和对照组显著提高断奶前犊牛空肠近端、空场远端和回肠乳糖酶活性（P〈0.05）,较3 g·d^-1和对照组显著提高断奶后犊牛十二指肠和回肠乳糖酶活性,较3 g·d^-1的2-甲基丁酸和对照组显著提高了断奶前后犊牛小肠各段脂肪酶、胰蛋白酶活性（P〈0.05）。断奶后犊牛小肠各段黏膜GHR和SGLT^-1m RNA的表达均显著低于断奶前。日粮添加2-甲基丁酸6和9 g·d^-1后,较3 g·d^-1的2-甲基?

英文摘要：

【Objective】 There are obvious changes observed in the development of the gastrointestine and its function of absorption and metabolism in pre- and post-weaning dairy calves. Especially, the development of the gastrointestine and even its future production performance which are influenced by the feeding and management of calves during the pre-weaning period. 2-methyl butyric acid is a kind of branched-chain short volatile fatty acids, mainly from the degradation of branched chain amino acids in the rumen, can be used as a control agent of ruminant animal gastrointestinal development. The aim of this study was to reveal the 2-methyl butyric acid on development mechanism of the small intestine by observing the effects of 2-methyl butyrate supplementation on the small intestine digestive enzymes activities and expression of growth hormone receptor（GHR） and sodium-glucose cotransporter（SGLT1） m RNA of small intestinal mucosa in dairy calves. 【Method】Thirty-two Holstein male calves（15-day-old） with similar body weight（44.7±0.3） kg were chosen and divided into four groups randomly. Calves in the control were fed milk in pre-weaning and calf-concentrate and alfalfa hay in the post-weaning period. Calves in treatments were supplemented 2-methylbutyrate at 3, 6 and 9 g per calf per day, respectively. All calves were weaned at 45 days of age. At 30 and 90 days of age, four calves from each group were selected and slaughtered before the morning feeding. Digesta and mucosa of duodenal, proximal jejunal, distal jejunal and ileal were collected to determine the activities of lactase, amylase, trypsase and lipase, and mR NA expression of GHR and SGLT^-1, respectively. 【Result】The results showed that lactase enzyme activity and mR NA expression of mucosal GHR and SGLT1 in every part of small intestine in post-weaning calves were lower than that in pre-weaning calves, while activities of amylase, lipase and trypsin in every part of the small intestine in post-weaning calves were higher than that of pre